Analysis of short-chain bioactive peptides by unified chromatography-electrospray ionization mass spectrometry. Part I. Method development

•Short-chain (three and five residues) linear and cyclic peptides.•Wide mobile phase gradients from 5 to 100% co-solvent in CO2.•4 stationary phases and 3 mobile phases examined.•Best method selected with Derringer desirability functions.•Good separation performance for positional and chain isomers.